Norethindrone and mestranol, the progestin and estrogen of the widely used oral contraceptive "Norinyl", will be fed either singly or in combination to ovariectomized guinea pigs. With such an experimental design, this study will identify which of these steroids, or the combined components, are responsible for the reduced tissue ascorbic acid levels established in women and quinea pigs. The major objective of this project is to elucidate the mechanism(s) responsible for the alteration of vitamin C metabolism. Data of recent studies indicated that the reduction of tissue ascorbic acid levels by oral contraceptive agents was caused by an increase in degradation rate. The activity of several major blood and liver enzymes involved in the catabolsim of vitamin C will be determined. In vitro studies will be performed to measure the degradation rate of ascorbic acid by plasma ceruloplasmin ascorbic acid oxidase and by plasma copper. The rate of degradation of dehydroascorbic acid to 2, 3-diketogulonic acid by liver homogenates and the catabolism of 2, 3-diketogulonic acid by liver decarboxylase will be determined. The in vitro reactions will be monitored by measuring the quantities of products formed or the remaining substrate.